In-line manufacture of carbon nanotubes

ABSTRACT

Mass production of carbon nanotubes (CNT) are facilitated by methods and apparatus disclosed herein. Advantageously, the methods and apparatus make use of a single production unit, and therefore provide for uninterrupted progress in a fabrication process. Embodiments of control systems for a variety of CNT production apparatus are included.

STATEMENT OF FEDERALLY SPONSORED RESEARCH

This invention was made with government support under grantDE-AR0000035/0001 awarded by the Unites States Department of Energy(ARPA-E). The United States government has certain rights in theinvention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to producing aligned carbon-nanotubeaggregates and, in particular, to methods and apparatus for producingcarbon-nanotube aggregates.

2. Description of the Related Art

Carbon nanotubes (hereinafter referred to also as “CNT” or “CNTs”) arecarbon structures that exhibit a variety of properties. Many of theproperties suggest opportunities for improvements in a variety oftechnology areas. These technology areas include electronic devicematerials, optical materials as well as conducting and other materials.

A known method for producing such CNTs is a chemical vapor depositionmethod (hereinafter referred to also as a “CVD method”). Prior art CVDmethods involve preparing a catalyst with a reducing gas (to eliminateoxidation), then bringing a carbon-containing gas (hereinafter referredto as “raw material gas”) into contact with a catalyst, (i.e., finemetal particles in a hot atmosphere of approximately 500 degrees Celsiusto 1,000 degrees Celsius). This results in CNTs with variations inaspects such as the type and arrangement. The CVD method has been usedto produce both single-walled carbon nanotubes (SWCNTs) and multiwallcarbon nanotubes (MWCNTs), and is capable of producing a large number ofCNTs aligned perpendicularly to a surface of the substrate.

One attempt to scale production of CNTs has been provided in U.S. Pat.No. 7,897,209, entitled “Apparatus and Method for Producing AlignedCarbon-Nanotube Aggregates.” The unit disclosed therein provides formass production of CNT. However, as the formation unit and the growthunit are provided separately, a reducing environment is used, and forother reasons, the process therein is complicated and requiresadditional handling. In short, there is room for improvement.

Thus, what are needed are methods and apparatus for production of carbonnanotubes in a high throughput environment. Preferably, the methods andapparatus offer reduced cost of manufacture, as well as an improved rateof production.

BRIEF SUMMARY OF THE INVENTION

Mass production of carbon nanotubes (CNT) are facilitated by methods andapparatus disclosed herein. Advantageously, the methods and apparatusmake use of a single production unit, and therefore provide foruninterrupted progress in a fabrication process. A control system for aCNT production apparatus is included.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features and advantages of the invention areapparent from the following detailed description taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a block diagram schematically showing an embodiment of afunctional configuration of a production apparatus;

FIG. 2 is a block diagram schematically showing another embodiment of afunctional configuration of a production apparatus;

FIG. 3 is a block diagram of aspects of a production apparatus; and

FIG. 4 is a block diagram depicting aspects of a control system for theproduction apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed are methods and apparatus for providing aggregates of carbonnanotubes (CNT). The techniques disclosed provide for a high degree ofcontrol over fabrication processes, and thus result in CNT that may bewell adapted (i.e., designed for) specific applications. As an overview,a base material is provided. A catalyst material is then disposed uponthe base material, and a carbonaceous material is deposited onto thecatalyst. As fabrication occurs in a substantially oxygen freeenvironment, problems associated with oxidation and a need for reductionare avoided. When practicing the various aspects of the techniquesdisclosed herein, manufacturers of CNT will realize efficient processesfor production of high quality CNT.

The techniques disclosed herein may be adjusted as necessary to provideCNT having desired properties. That is, the processes may be controlledwith regard for favoring properties such as density, surface area,length, a number of walls, composition (i.e., metallic or non-metallic),end properties (i.e., open end or closed end) and the like.

Reference may be had to FIG. 1 for an overview of an exemplaryembodiment. In FIG. 1, non-limiting aspects of a process for fabrication10 of CNT are provided. In this embodiment, the process for fabrication10 includes a first step 11 where base material is loaded into afabricator (also referred to as a “production apparatus” and by othersimilar terms). In a second step 12, a layer of a catalyst is applied tothe base material. In a third step 13, carbonaceous material isprogressively deposited onto the catalyst layer and the CNT are grown.In a fourth step 14, the CNT are cooled for offloading and subsequentuse.

An exemplary apparatus is provided for mass production of the CNT. Invarious embodiments, the apparatus is arranged to provide rigorousenvironmental controls (e.g., control over temperature, atmosphericcontent and/or pressure, etc, . . . ). In general, the CNT product isproduced in an ongoing (i.e., uninterrupted or continuous) process. Bycontrolling the production environment throughout the process, and byvarying aspects of the production environment as needed during theprocess, it is possible to produce CNT that exhibit desired properties.

As one might imagine, the process requires considerable equipment andcontrols and therefore that the description of these four steps is anoversimplification. In order to provide some context for greaterexplanation of each step (11-14), as well as additional embodiments,some definitions, parameters, properties and such are now presented.

A machine that is referred to as a “production apparatus,” “fabricator”or by any other similar term or terms herein generally includescomponents as necessary or desired for fabrication of the CNT. Exemplarycomponents that are included in the production apparatus includecomponents as necessary to perform described functions. Exemplary andnon-limiting examples of components that may be included include atleast one pump, valve, electrical conduit, gas conduit, power supply,gas supply (including supplies of inert gas, carbonaceous gas and thelike), water supply, nozzle, intake, outlet, vent, exhaust, fan,material moving apparatus (such as a conveyer belt, drive system and thelike), heating element (such as a resistive heating element), heatexchanger (or other form of refrigeration), shutter, door, servo, motor,sensor (electrical, temperature, pressure, gas, optical, etc, . . . ),transducer, controller, human interface, computer interface, processor,data storage, memory, bus, computer executable code for governingoperation of the machine, and others as may be needed by a machineoperator, manufacturer or designer. In short, the various technologiesthat support and enable the processes described herein are considered tobe well known, and generally not a part of the invention disclosedherein. Accordingly, given the many embodiments and variations ofequipment for implementing the teachings herein, discussion of suchequipment is generally limited to some of the aspects that may affectgeneration of the CNT aggregate.

As used herein “aligned CNT aggregate,” “CNT aggregate,” and othersimilar terms generally refer to a structure in which a large number ofCNTs are aligned or oriented in a common manner. In some embodiments,specific surface area (SA) of the aligned CNT aggregate is not less than300 m²/g when the CNTs are mostly unopened. In other embodiments, thesurface area (SA) is not less than 1,300 m²/g, such as when the CNTs aremostly opened.

In some embodiments, the weight density (ρ_(w)) ranges from 0.002 g/cm³to 0.2 g/cm³. If the weight density (ρ_(w)) is less than 0.2 g/cm³,there will be a weakening in binding of CNTs constituting the alignedCNT aggregate.

In order for the CNT aggregate to exhibit common orientation and a largespecific surface area (SA), the height of the CNT aggregate may be in arange of not less than 10 μm to not greater than 1 cm. A height of notless than 10 μm leads to an improvement in orientation. Alternatively, aheight of not greater than 1 cm makes it possible to improve thespecific surface area, because such a height makes rapid generationpossible and the adhesion of carbonaceous impurities is thereforecontrolled.

The term “base material” refers to a member that is capable ofsupporting a catalyst for carbon nanotubes on a surface thereof, and canmaintain its shape even at a high temperature (for example, atemperature that is not lower than 400 degrees Celsius). Any type ofbase material that has been proven to be usable for production of CNTsmay be used. Non-limiting examples of materials include: metals such asiron, nickel, chromium, molybdenum, tungsten, titanium, aluminum,manganese, cobalt, copper, silver, gold, platinum, niobium, tantalum,lead, zinc, gallium, germanium, arsenic, indium, phosphor, and antimony;alloys and oxides containing these or other suitable materials;nonmetals such as silicon, quartz, glass, mica, graphite, and diamond;and ceramic. Generally, the metal materials are lower in cost thansilicon and ceramic. In particular, a Fe—Cr (iron-chromium) alloy, aFe—Ni (iron-nickel) alloy, a Fe—Cr—Ni (iron-chromium-nickel) alloy, andthe like are suitable. The base material may take the form of a thinfilm, a block, or a powder, as well as a flat plate. However, inparticular, such a form that the base material has a large surface areafor its volume is advantageous to mass production.

The term “carburizing prevention layer” generally refers to a layer onthe base material. The base material may have a carburizing preventionlayer formed on either a front or back surface thereof. In someembodiments, the base material includes a carburizing prevention layerformed on each of the front and back surfaces thereof. The forming maybe realized through techniques such as, for example, sputtering.Generally, the carburizing prevention layer is a protecting layer forpreventing the base material from being carburized and thereforedeformed in the step of generating carbon nanotubes.

In some embodiments, the carburizing prevention layer is composed of ametal or ceramic material (the ceramic material being highly effectivein preventing carburizing). Examples of suitable metal include copperand aluminum. Examples of suitable ceramic material include: oxides suchas aluminum oxide, silicon oxide, zirconium oxide, magnesium oxide,titanium oxide, silica alumina, chromium oxide, boron oxide, calciumoxide, and zinc oxide; and nitrides such as aluminum nitride and siliconnitride. It is noted that aluminum oxide and silicon oxide are both veryeffective in preventing carburizing.

As used herein, a “catalyst” is provided on the base material or thecarburizing prevention layer. Any type of catalyst that has been provento be usable for production of CNTs can be used. Non-limiting examplesof the catalyst include iron, nickel, cobalt, molybdenum, a chloridethereof, an alloy thereof, and a complex or layer thereof with aluminum,alumina, titania, titanium nitride, or silicon oxide. Other non-limitingexamples include an iron-molybdenum thin film, an alumina-iron thinfilm, an alumina-cobalt thin film, an alumina-iron-molybdenum thin film,an aluminum-iron thin film, and an aluminum-iron-molybdenum thin film.The catalyst can be used in a range of quantities that has been provento be usable for production of CNTs. For example, in some embodimentsmaking use of iron, a thickness of a film formed may be in a range ofnot less than 0.1 nm to not greater than 100 nm. In some otherembodiments, the thickness of the iron may be not less than 0.5 nm tonot greater than 5 nm. In some further embodiments, the thickness of theiron may be 0.8 nm to not greater than 2 nm.

It is possible to apply a dry process to the formation of the catalystonto the surface of the base material. For example, a sputteringevaporation method may be used. Other techniques such as any one or moreof cathodic arc deposition, sputter deposition, ion beam assisteddeposition, ion beam induced deposition and electrospray ionization maybe used as appropriate. Further, it is possible to form the catalystinto any shape with concomitant use of patterning obtained by applyingwell-known photolithography, nanoprinting or the like.

In one embodiment, it is possible to arbitrarily control the shape of analigned CNT aggregate. This may be achieved, for example, according topatterning of the catalyst formed on the substrate and controlling thegrowth time for CNTs. As a result, the aligned CNT aggregate takes athin-film shape, a cylindrical shape, a prismatic shape, or any othercomplicated shape. In particular, in the shape of a thin film, thealigned CNT aggregate has an extremely small thickness (height) ascompared with its length and width; however, the length and width can bearbitrarily controlled according to the catalyst patterning, and thethickness can be arbitrarily controlled according to the growth time forCNTs that constitute the aligned CNT aggregate. Accordingly, furthertechniques for adapting the catalyst are provided herein.

In general, a “reducing gas” is not required by the teachings herein. Areducing gas is commonly used in the prior art to provide for reducingthe catalyst. The reducing gas may include any material that is in agaseous state at a growth temperature. The reducing gas may also be usedfor stimulating the catalyst to become fine particles suitable for thegrowth of CNTs as well as to improve the activity of the catalyst. Anexample of the reducing gas is a gas having reducing ability, such ashydrogen gas, ammonium, water vapor, or a mixture thereof. While thereducing gas is generally used to overcome oxidation, the processesdisclosed herein are substantially oxidation free.

A “raw material gas” is generally used to supply raw (i.e.,carbonaceous) material for generation of the CNTs. Any type of rawmaterial that has been proven to be usable for production of CNTs can beused. In general, raw-material carbon sources that are gaseous at thegrowth temperature can be used. Among them, hydrocarbons such asmethane, ethane, ethylene, propane, butane, pentane, hexane,heptanepropylene, and acetylene are suitable. In addition, loweralcohols such as methanol and ethanol, acetone, low-carbonoxygen-containing compounds such as carbon monoxide, and mixturesthereof can be used. Further, the raw material gas may be diluted withan inert gas.

“Inert gas” is a gas that may be included in the production processes,and only needs to be a gas that is inert at the temperature at whichCNTs grow. Generally, “inert” is considered to be a property of the gaswhere it does not react substantially with growing of the CNTs. Any typeof inert gas that has been proven to be usable for production of CNTscan be used. Non-limiting examples of inert gas are helium, argon,hydrogen, nitrogen, neon, krypton, carbon dioxide, chlorine and mixturesthereof.

A “catalyst activation material” may be used in various embodiments. Theaddition of the catalyst activation material makes it possible toimprove efficiency in the production of carbon nanotubes and the purityof the carbon nanotubes. In general, the catalyst activation materialmay be characterized as an oxygen-containing substance that does nosignificant damage to CNTs at the growth temperature. Effective examplesother than water include: low-carbon oxygen-containing compounds such ashydrogen sulfide, oxygen, ozone, acidic gases, nitrogen oxide, carbonmonoxide, and carbon dioxide; alcohols such as ethanol and methanol;ethers such as tetrahydrofuran; ketones such as acetone; aldehydes;esters; nitrogen oxide; and mixtures of thereof.

In general, the catalyst activation material only needs to be added insmall amounts, however, there are no particular limits on amounts to beadded. As an example, in some embodiments, when the catalyst activationmaterial is water, the catalyst activation material is added in a rangeabout 10 ppm to about no more than 10,000 ppm, in some of theseembodiments in amounts not less than 50 ppm to not greater than 1,000ppm, and in some of these embodiments in amounts not less than 100 ppmto not greater than 700 ppm.

With the addition of the catalyst activation material, the activity ofthe catalyst is enhanced and the longevity of the catalyst is extended.When the catalyst activation material is added the growth of CNTscontinues for a longer period of time and the growth rate increases aswell. As a result, a CNT aggregate with a marked increase in height isobtained.

An “environment of high-carbon concentration” refers to a growthatmosphere in which a proportion of the raw material gas to the totalflow is approximately 2% to about 20%. This generally refers to anenvironment where excess carbon is present, which results inin-efficient growth of the CNTs. That is, for example, an environment ofhigh-carbon concentration may induce deactivation of the catalyst.

Since the activity of the catalyst is improved by the catalystactivation material, the activity of the catalyst will continue even insome environments of high-carbon concentration. Thus, the growth rate ofthe CNT may be remarkably improved.

With regard to furnace pressure, in various embodiments, the furnacepressure is not lower than 10² Pa and not higher than 10⁷ Pa (100 inatmospheric pressure). In some embodiments, the furnace pressure is notlower than 10⁴ Pa and not higher than 3×10⁵ Pa (3 in atmosphericpressure).

The reaction temperature at which the CNTs are synthesized may bedetermined with consideration of various parameters, such as propertiesof the metal catalyst, the raw-material carbon source and the furnacepressure. In embodiments making use of catalyst activation material, thereaction temperature is generally set for a temperature range such thatthe catalyst activation material will operate adequately.

Specifically, in the case of use of water as the catalyst activationmaterial, it is preferable that the reaction temperature be in a rangeof 400 degrees Celsius to 1,000 degrees Celsius. At 400 degrees Celsiusor lower, the catalyst activation material does not express its effect.At 1,000 degrees Celsius or higher, the catalyst activation materialreacts with the CNTs.

Alternatively, in the case of use of carbon dioxide as the catalystactivation material, it is preferable that the reaction temperature bein a range of about 400 degrees Celsius to about 1,100 degrees Celsius.Generally, at a temperature of 400 degrees Celsius or lower, thecatalyst activation material does not express its effect. At 1,100degrees Celsius or higher, the catalyst activation material reacts withthe CNTs.

As used herein, the terms “growth step,” “deposition step”, “CVD” andsimilar terms refer to a process for synthesizing a CNT aggregate.Generally, this step involves providing an environment surrounding thecatalyst that includes a carbonaceous component, such as the rawmaterial gas, and heating at least one of the environment, the rawmaterial gas and the catalyst. This results in the CNT aggregate.

As used herein, a “cooling step” is a step of cooling down the CNTaggregate, the catalyst, and the base material. In some embodiments, thecooling step is performed in the presence of an inert gas. That is,after the growth step, the CNT aggregate, the catalyst, and the basematerial are high in temperature, and as such, will be oxidized whenplaced in the presence of oxygen. Oxidation is substantially preventedby cooling down the CNT aggregate, the catalyst, and the base materialto a temperature where oxidation processes are substantially limited. Insome examples, cessation of cool down is at or below a temperature ofabout 200 degrees Celsius.

A “load section” (see reference number 11 in FIG. 1) generally includesa set of devices for preventing the outside air from flowing into theproduction apparatus. That is, in operation, the load section providescomponents for loading the base material. Generally, the base materialis loaded onto a conveyance device. Once loaded, oxygen is expelled fromthe load section (by at least one of a negative pressure exhaust and apressurizing with inert gas). In some embodiments, the load section isisolated by at least one of a door, a shutter or other mechanicaldevice.

Once environmental control has been established in the load section(i.e., once the load section is substantially or adequatelyoxygen-free), the base material is advanced to a catalyst applicationsection (see reference number 12 in FIG. 1). Like the load section, thecatalyst application section of the production apparatus is subject toenvironmental control (i.e., is substantially or adequatelyoxygen-free). Once the base material is oriented in the catalystapplication section, the catalyst is applied to the base material. Oneembodiment for applying the catalyst includes sputtering the catalystonto the base material.

Once an adequate layer of catalyst has been applied to the base material(which may include the carburizing prevention layer disposed thereon), aCNT substrate is realized. The substrate may be characterized as a basematerial having a layer of catalyst material disposed thereon.Advantageously, as the substrate has been produced in a substantially oradequately oxygen-free environment, the catalyst is not subject to anysignificant oxidation. Thus, the substrate is prepared for growth of theCNT.

Once the substrate has been prepared, in some embodiments, it is movedinto a buffer section (see reference number 13 in FIG. 1). In variousembodiments, the buffer section provides for at least one of adjustingand changing at least one of pressure, temperature and gas in theenvironment surrounding the substrate. The buffer section may alsoprovide other functionality, such as loading or reorienting thesubstrate.

The substrate may then be transferred to a carbon deposition section(see reference number 14 in FIG. 1). The deposition section has afunction of synthesizing the CNT aggregate by causing the environmentsurrounding the catalyst, to be an environment of a raw material gas andby heating at least one of the catalyst and the raw material gas.Specific examples of the deposition section include a furnace in whichthe environment of the raw material gas is retained, a raw material gasinjection section for injecting the raw material gas, and a heater forheating at least one of the catalyst and the raw material gas. Theheater may be any type of heater that is capable of heating adequately.In some embodiments, the heater heats to a temperature in a range ofbetween about 400 degrees Celsius and about 1,100 degrees Celsius.Non-limiting examples of the heater include a resistance heater, aninfrared heater, and an electromagnetic induction heater.

In some embodiments, the deposition section also includes a sub-sectionfor addition of the catalyst activation material. Generally, thesub-section to add the catalyst activation material is equipped toprovide the activation material directly into the raw material gas, orto add the catalyst activation material directly to the environmentsurrounding the catalyst inside of the deposition section. The catalystactivation material may be supplied in a variety of ways, including bysupplying the catalyst activation material through a bubbler, supplyingthe catalyst activation material by vaporizing a solution containing thecatalyst activation material, supplying the catalyst activation materialas it is in a gaseous state, and supplying the catalyst activationmaterial by liquefying or vaporizing a solid catalyst activationmaterial. The sub-section may include a supply system using variousapparatuses such as at least one of a vaporizer, a mixer, a stirrer, adiluter, a pump, and a compressor. Some embodiments include a device formeasuring a concentration of the catalyst activation material in thesub-section. Through feedback and engineering controls, a stable supplyof the catalyst activation material can be ensured.

Following growth of the CNT, and while the CNT aggregate remains in atemperature range that is at or about the temperature range used forfabrication, oxidation of the CNT aggregate remains a concern.Accordingly, the CNT aggregate is transferred from the depositionsection to a cooling section (see reference number 15 in FIG. 1).

The cooling section provides for cooling down CNT aggregate and thesubstrate on which the CNT aggregate has grown. The cooling section hasa function of exerting antioxidant and cooling effects on the CNTaggregate, the catalyst, and the base material after deposition has beencompleted. Exemplary apparatus for the cooling section include areceiving area for receiving the substrate and CNT aggregate, thereceiving area disposed within a volume in which an inert gas isretained. The volume may include, for example, inlets (and outlets) forproviding a flow of lower temperature inert gas, at least one coolingconduit disposed in the volume, the cooling conduit for carrying aliquid coolant (such as water) as well as any other similar apparatussuited for conveying a cooling media. Additional apparatus may beincluded external to the cooling section, such additional apparatusincluding, for example, at least one heat exchanger that is capable ofdissipating heat carried from the cooling unit.

Having thus introduced various components of the production apparatus,certain additional aspects are now discussed.

The fabrication techniques disclosed herein generally do not require theuse of a reducing gas. That is, the fabrication techniques result incatalyst materials that are prepared substantially free of oxidation.Accordingly, operation of the production apparatus is generallyperformed in a manner that limits intrusion of oxygen (such as in theform of ambient air) into the production area. Thus, the various stepsdiscussed herein may be performed in the presence of at least an inertgas (which is provided, among other things, to displace any oxygen).

Thus, the production apparatus may be configured to ensure a relativelyoxygen free environment. That is, various engineering controls (many ofwhich are introduced above), may be arranged to ensure maintenance of adesired environment. As in the case of FIG. 1, discussion of FIG. 2 isin a functional format.

Referring now to FIG. 2, there are shown aspects of an additionalembodiment of a production apparatus. In this embodiment, anintermediate step is included. That is, after the second step 12 wherethe catalyst is disposed onto the base material, and before the thirdstep 13 of FIG. 1, another step 21 is performed. In the another step 21,a plasma is provided. More specifically, the substrate (i.e., the basematerial with the catalyst disposed thereon) is subjected to a plasmatreatment. As with application of the catalyst, the another step 21 isperformed without a need for creating a reducing environment, such as byaddition of a reducing gas. By controlling the time and power of theplasma, morphology of the catalyst may be adjusted. Specifically, inthis step, the plasma may be controlled to result in desired changes tothe catalyst. Exemplary changes include modifications to particle sizeas well as density of particles in the catalyst. Following the anotherstep 21 where surface treatment of the catalyst is performed, thesubstrate proceeds into the deposition step. Although not depicted inFIG. 2, some embodiments may also include at least one buffer section(as described with regard to FIG. 1).

In general, in the embodiments shown in FIGS. 1 and 2, the processbegins and ends with human interaction (for example, loading basematerial, unloading finished product). However, in other embodiments,additional automated steps or functions may take place.

FIG. 3 depicts aspects of an embodiment of a production apparatus 100.In this example, the production apparatus 100 includes a loader section31, a sputterer section 32, a plasma section 33, a chemical vapordeposition (CVD) section 34 and a cooler section 35. During operation,the base material 30 is loaded into the production apparatus via theloader section 31. The base material 30 progresses through the sputterersection 32, the plasma section 33, the chemical vapor deposition (CVD)section 34 and the cooler section 35 on a conveyor-belt to emerge as afinished product. That is, the base material 30 emerges from theproduction apparatus 100 with a catalyst layer 36 disposed thereon andcarbon nanotube aggregate 37 disposed on the catalyst layer 36. In someof these embodiments, the conveyor-belt (not shown) is actually aplurality of conveyor belts, thus permitting fine control over the speedthe base material 30 is conveyed through each section (31-35).

Each of the foregoing sections (31-35) may make use of any particulartype of equipment that is deemed appropriate, and is only limited bypractical considerations such as ability to operate at elevatedtemperatures. For example, a “gas shower” may be used in the CVD section34 to provide for uniform dispersion of the carbonaceous material.

In general, the term “gas shower” refers to a volume into which at leastone gaseous material is introduced. Generally, the gas shower providesfor fulfillment of goals such as, for example, isolation of a firstvolume in the production apparatus 100 from a second volume in theproduction apparatus 100 and the like. The gas shower may include a“drain” (i.e., an exhaust). The drain may be at a negative pressure, andadapted for substantially pulling out the at least one gaseous materialfrom the volume of the gas shower. A gas shower may make use of knowncomponents to achieve the intended design and/or functionalitydetermined by at least one of a designer, manufacturer and user.

The carbon nanotube aggregate 37 may be harvested in a variety of ways(which are not presented herein). Following the harvesting, in someembodiments, an etching or other process may be used to remove thecatalyst layer 36 from the base material 30. The base material 30 maythen be suitably prepared and recycled into production.

Referring now to FIG. 4, aspects of an exemplary control system 40 forthe production apparatus are shown. In this example, the control system40 includes a plurality of sensors 41. The sensors 41 may includeapparatus for measuring temperature, gas, feed rate, optical propertiesand the like. In short, any process dynamic that is useful forcontrolling the production process. The sensors 41 communicate with atleast one processor 43 through a communications link 46. Any type ofcommunications link 46 may be used, including wired and wireless links.The at least one processor 43 in turn communicates with computingcomponents 44 (such as memory, data storage, a power supply, a clock,machine executable program instructions stored on machine readable mediain the form of software, and other such components) as well as at leastone interface 45. The at least one interface 45 may include a keyboard,a video display, a mouse, a network adapter, a printer and other similarinterface components. These components of the control system 40 provideinput to controls 42 (such as a servo, a motor, a valve, a heater, a gassupply, an operator and any other type of process control) to modify theproduction process.

The control system 40 may be used for governing production apparatus 100such as those of embodiments described herein, as well as otherproduction apparatus. For example, the control system 40 may be usedwith systems that include a formation unit and a separate growth unit aswell as a transfer mechanism. In short, the control system 40 is highlycustomizable and may be used to control virtually any system designedfor fabrication of carbon nanotube aggregate. Aspects that may becontrolled by the control system 40 include, without limitation,temperature, flow rate, conveyor speed, processes related to layering(such as layer thickness, control over combinations of materials (suchas gases, etc, . . . )) and the like.

As practicable, the control system 40 provides for in-line (i.e.,real-time) quality control. By way of example, the control system 40 mayinclude an optical metrology system that measures at least one propertyof at least one of the catalyst layer 36 and the carbon nanotubeaggregate 37. Exemplary properties include thickness, density, surfaceappearance, etc, . . . . When included in the production apparatus 100,the optical metrology system may provide information to a user or othersimilar output, so as to ensure adequate layering of materials, earlyrejection of defective materials, etc, . . . .

Examples of materials for components of the production apparatus 100include materials capable of resisting high temperatures, such asquartz, heat-resistant ceramic, heat-resistance alloys. However, theheat-resistance alloys are preferable in terms of precision ofprocessing, degree of freedom of processing, and cost. Examples of theheat-resistance alloys include heat-resistant steel, stainless steel,and nickel-based alloys. In general, heat-resistant steel refers tosteel that contains Fe in major proportions and other alloys inconcentrations of not greater than 50%, and stainless steel refers tosteel that contains approximately not less than 12% of Cr. Further,examples of the nickel-based alloys include alloys obtained by addingMo, Cr, Fe, and the like to Ni. Specifically, SUS 310, Inconel 600,Inconel 601, Inconel 625, Incoloy 800, MC Alloy, Haynes 230 Alloy may beuseful in consideration of heat resistance, mechanical strength,chemical stability, and low cost.

The presence of carbon contaminants that adhere to the wall surfaces andother components of the production apparatus when CNTs are synthesizedcan be reduced by various techniques. That is, by way of example,interior facing components such as the inner walls of the furnacesand/or the components for use in the furnaces are fabricated from ametal, e.g., a heat-resistant alloy and by finishing the interiorsurfaces. This provides for, among other things, continued productionoutput while limiting deterioration in quality of the resulting alignedCNT aggregates.

For example, in some embodiments, reduction of surface contaminants maybe achieved by treatment of components internal to the productionapparatus. As an example, internal components may be passivated withsilicon. Exemplary techniques for treatment of the internal componentsare disclosed in various U.S. patents. A first patent is U.S. Pat. No.6,444,326, entitled “Surface modification of solid supports through thethermal decomposition and functionalization of silanes.” This patentteaches a method of modifying the surface properties of a substrate bydepositing a coating of hydrogenated amorphous silicon on the surface ofthe substrate and functionalizing the coated substrate by exposing thesubstrate to a binding reagent having at least one unsaturatedhydrocarbon group under pressure and elevated temperature for aneffective length of time. The hydrogenated amorphous silicon coating isdeposited by exposing the substrate to silicon hydride gas underpressure and elevated temperature for an effective length of time.

A second patent is U.S. Pat. No. 6,511,760, entitled “Method ofpassivating a gas vessel or component of a gas transfer system using asilicon overlay coating.” This patent teaches a method of passivatingthe interior surface of a gas storage vessel to protect the surfaceagainst corrosion. The interior surface of the vessel is firstdehydrated and then evacuated. A silicon hydride gas is introduced intothe vessel. The vessel and silicon hydride gas contained therein areheated and pressurized to decompose the gas. A layer of silicon isdeposited on the interior surface of the vessel. The duration of thesilicon depositing step is controlled to prevent the formation ofsilicon dust in the vessel. The vessel is then purged with an inert gasto remove the silicon hydride gas. The vessel is cycled through thesilicon depositing step until the entire interior surface of the vesselis covered with a layer of silicon. The vessel is then evacuated andcooled to room temperature.

A third patent is U.S. Pat. No. 7,070,833, entitled “Method for chemicalvapor deposition of silicon on to substrates for use in corrosive andvacuum environments.” This patent teaches a method of passivating thesurface of a substrate to protect the surface against corrosion, thesurface effects on a vacuum environment, or both. The substrate surfaceis placed in a treatment environment and is first dehydrated and thenthe environment is evacuated. A silicon hydride gas is introduced intothe treatment environment, which may be heated prior to the introductionof the gas. The substrate and silicon hydride gas contained therein areheated, if the treatment environment was not already heated prior to theintroduction of the gas and pressurized to decompose the gas. A layer ofsilicon is deposited on the substrate surface. The duration of thesilicon depositing step is controlled to prevent the formation ofsilicon dust in the treatment environment. The substrate is then cooledand held at a cooled temperature to optimize surface conditions forsubsequent depositions, and the treatment environment is purged with aninert gas to remove the silicon hydride gas. The substrate is cycledthrough the silicon depositing step until the surface of the substrateis covered with a layer of silicon. The treatment environment is thenevacuated and the substrate cooled to room temperature.

Each of U.S. Pat. Nos. 6,444,326, 6,511,760, and 7,070,833 areincorporated by reference herein in their entirety.

That is, each of these patents teach methods that are suited fortreating components exposed to the growth and/or production environmentswithin the production apparatus.

In short, components of the furnace(s) may be passivated or otherwisetreated as appropriate in advance of production. These components may beperiodically evaluated for ability to limit buildup of contaminants. Asappropriate, a user may renew components or replace components to ensurecontinued performance.

Having disclosed aspects of embodiments of the production apparatus andtechniques for fabricating aggregates of carbon nanotubes, it should berecognized that a variety of embodiments of apparatus and methods may berealized. Accordingly, while the invention has been described withreference to exemplary embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe invention. For example, steps of fabrication may be adjusted, aswell as techniques for layering, materials used and the like. Manymodifications will be appreciated by those skilled in the art to adapt aparticular arrangement or material to the teachings of the inventionwithout departing from the essential scope thereof. Therefore, it isintended that the invention not be limited to the particular embodimentdisclosed as the best mode contemplated for carrying out this invention.

1. A method of producing an aggregate of vertically aligned carbonnanotubes, the method comprising: (a) loading a base material into acontrolled environment; (b) disposing a catalyst onto the base materialto provide a substrate in an environment having an oxygen concentrationlow enough to substantially prevent oxidation of the substrate; (c)subjecting the substrate to a carbonaceous raw material gas and heatingat least one of the raw material gas and the substrate for growing theaggregate onto the substrate; and (d) cooling the aggregate in anenvironment having an oxygen concentration low enough to substantiallyprevent oxidation of the aggregate during the cooling; wherein steps (a)to (d) are performed in the controlled environment comprising chamberssequentially connected in a manner that limits the exposure of the basematerial and any catalyst, substrate, and aggregate disposed thereon tocontamination between each step.
 2. The method of claim 1, furthercomprising disposing a carburizing prevention layer on at least one ofthe base material and the catalyst.
 3. The method of claim 1, whereindisposing the catalyst comprises using at least one of sputteringevaporation, cathodic arc deposition, sputter deposition, ion beamassisted deposition, ion beam induced deposition and electrosprayionization.
 4. The method of claim 1, further comprising treating thesubstrate with a plasma.
 5. The method of claim 1, further comprisingsubjecting the substrate to a catalyst activation material during thegrowing of the aggregate.
 6. The method of claim 5, further comprisingadding the catalyst activation material to the raw material gas.
 7. Themethod of claim 1, further comprising selecting a production apparatuscomprising components treated to limit buildup of contaminants.
 8. Themethod of claim 7, wherein treatment of the components comprisespassivating the components with at least one passivation material. 9.The method of claim 8, wherein the passivation material comprises asilicon containing material.
 10. An apparatus for fabricating anaggregate of vertically aligned carbon nanotubes, the apparatuscomprising: a first section adapted for receiving a substrate anddisposing a catalyst thereon; a second section adapted for growing theaggregate onto the substrate; at least one of the first section and thesecond section comprising at least component that has been passivated tosubstantially limit deposition of carbon thereon.
 11. The apparatus ofclaim 10, wherein the at least one component has been passivated with atleast one form of silicon.
 12. The apparatus of claim 10, whereinpassivation has been completed by at least one cycle of deposition of asilicon containing compound onto the at least one component and heatingthe at least one component.
 13. The apparatus of claim 10, wherein atleast one of the first section and the second section are fabricatedfrom components substantially capable of resisting high temperatures.14. The apparatus of claim 10, further comprising a control system forcontrolling the fabricating.
 15. The apparatus of claim 10, furthercomprising components for disposing the catalyst by at least one ofsputtering, chemical vapor deposition (CVD), thermal deposition andion-beam deposition.
 16. An apparatus for fabricating an aggregate ofvertically aligned carbon nanotubes, the apparatus comprising: a firstsection adapted for receiving a substrate and disposing a catalystthereon; a second section adapted for growing the aggregate onto thesubstrate; and a control system for controlling the fabricating.
 17. Theapparatus of claim 16, further comprising at least one sensor adaptedfor monitoring the fabricating and providing monitoring information. 18.The apparatus of claim 16, wherein the control system comprises a set ofcomputer executable instructions stored on machine readable media, theinstructions comprising instructions for controlling at least one aspectof the fabricating.
 19. The apparatus of claim 18, wherein the aspectcomprises at least one of: disposing of the catalyst; a temperature; apressure; a feed rate; a setting for at least one of a valve, a heater,a gas supply, a motor and a servo; an order of steps in the fabricating;an optical system and rejection of defective materials.
 20. The methodof claim 1, wherein, during the performance of steps (a) to (d), thechambers are sequentially connected in a manner that substantiallyprevents the exposure of the base material and any catalyst, substrate,and aggregate disposed thereon to room air between each step.